A particular example of such a machine is already known, and is described in particular in FIG. 1 of FR 2 888 859.
That machine serves in particular to implement the “soil-mixing” technique, which consists in making successive panels by mixing the cut soil with a cement in situ in the trench, or more generally mixing it with a binder, the soil/binder mixture subsequently forming the wall. That technique is in particularly widespread use for making retaining walls or sealing screens.
That machine may also be used for making walls that are buried in the ground, of the diaphragm wall type. That consists in forming successive trench portions in the ground with the help of such an excavation machine, and in filling the trench as made in that way with cement or concrete.
In order to make trench portions, the carriage slides along the mast from its top end down to its bottom end. In other words, the stroke of the carriage corresponds substantially to the length, or height, of the mast. Insofar as the bar, usually referred to as a “kelly” bar by the person skilled in the art, is held by the carriage, it can be understood that the stroke of the kelly bar is likewise substantially equal to the height of the mast. It therefore follows that the machine is suitable for making trench portions of a depth that can be no greater than the height of the mast.
In other words, the excavation depth of the machine is limited by the height of the mast. That presents a drawback, since in practice, the length of excavation machine masts is limited to about 20 meters (m) even though it is sometimes desirable to be able to reach excavation depths that are considerably deeper.
It is known that one solution to that problem is to use a bar or kelly bar of length that is longer than the length of the mast.
That apparently simple solution is difficult to implement since, at present, it is difficult to raise the bar so as to mount it on the mast, with the mast being in the vertical position and the bar possibly being as much as thirty meters long.
More generally, there is the problem of mounting the bar on the mast, regardless of the length of the bar. At present, it is necessary to make use of external hoist means for mounting the bar on the mast. Furthermore, connecting hydraulic hoses for powering the motors of the excavation tool is difficult and dangerous to undertake since operators need to take action high above the ground.